Jeffrey P. Calame

A gyrotron-traveling-wave tube amplifier experiment with a ceramic loaded interaction region

The design and experimental study of a 35-GHz gyrotron-traveling-wave tube (gyro-TWT) amplifier operating in the circular TE/sub 01/ mode at the fundamental cyclotron harmonic are presented. The interaction circuit in this experiment consisted of a new type of ceramic loading that provided the required loss for stable operation. A saturated peak power of 137 kW was measured at 34.1 GHz, corresponding to a saturated gain of 47.0 dB and an efficiency of 17%, with a -3-dB bandwidth of 1.11 GHz (3.3%). Peak output powers in the range of 102.1 to 148.6 kW with -3-dB bandwidths of 1.26 and 0.94 GHz, respectively, were measured by varying the operating parameters. The gyro-TWT was found to be zero-drive stable at these operating points, demonstrating that ceramic loading is a highly effective means of suppressing spurious oscillations in gyro-TWTs. This type of ceramic loading has the added advantage of being compatible with high average power operation.

Finite difference simulations of permittivity and electric field statistics in ceramic-polymer composites for capacitor applications

Finite difference quasielectrostatic modeling is used to predict the complex dielectric permittivity of barium titanium oxide (BTO)—polymer composites of interest for capacitor applications. The simulations explore the effects of the microstructural arrangement of spherical ceramic particles, the volume filling fraction of ceramic, and the type of polymer on the composite permittivity. For composites with randomly positioned ceramic particles, a soft percolation regime is found between volume filling fractions of 0.35 and 0.5 that leads to a more gradual growth in permittivity compared to ordered arrangements of particles. For BTO dispersed in a representative relaxor ferroelectric polymer, dielectric constants as high as 300 are predicted at a filling fraction of 0.45. Electric field statistics inside the composites are also computed, and localized intensification factors in the range of three to eight times the applied field are predicted, with an incrementally linear growth in high-field probability wi...

Gyrotron-traveling wave-tube circuits based on lossy ceramics

The gyro-traveling wave tube (gyro-TWT) is a microwave amplifier with simultaneous high power, high frequency, and broad bandwidth capabilities. Techniques for providing a controlled loading of the TE/sub 01/ cylindrical-guide operating mode of a 35 GHz gyro-TWT using monolithic, lossy ceramic structures are presented. The loading scheme, which also suppresses spurious backward-wave oscillations in the TE/sub 11/, TE/sub 21/, and TE/sub 02/ modes, is based on a sequence of alternating ceramic cylindrical shells and metal rings to form the electron beam tunnel. Design techniques for achieving optimal performance and methods for reducing the sensitivity to temperature-induced variations in ceramic dielectric properties are presented.

A TE/sub 11/ K/sub a/-band gyro-TWT amplifier with high-average power compatible distributed loss

Current amplifier research at the Naval Research Laboratory Vacuum Electronics Branch emphasizes techniques to extend the bandwidth and average power capability of gyro devices for millimeter wave radar applications. This paper will discuss the implementation of a wideband high-gain gyro-traveling wave tube amplifier design, with a measured peak output power of 78 kW, gain /spl sim/60 dB, and a 3-dB bandwidth of 4.2 GHz (12%) at 52 kW in K/sub a/-band. The 3-dB saturated bandwidth at 70 kW is 6 GHz (17%), which is also the instantaneous bandwidth with appropriately tailored input power (e.g., gain equalizer). The amplifier operates in the TE/sub 11/ mode and for stabilization employs a high-average power compatible diffractive loading technique.

Development and testing of a high-average power, 94-GHz gyroklystron

The development of a 10-kW average power, 94-GHz gyroklystron amplifier is described. This average power was obtained with 11% radio frequency (RF) duty factor and 92-kW peak power in the TE/sub 01/ circular cavity mode. The instantaneous bandwidth was 420 MHz, and the efficiency was 33.5%. Low-duty-factor testing also yielded a peak power of as much as 115 kW with 600-MHz instantaneous bandwidth. This development effort was carried out over the past three years and represents record average power performance in an amplifier at this frequency.

Experimental investigation of a high power, two-cavity, 35 GHz gyroklystron amplifier

Experiments on a two-cavity gyroklystron amplifier are performed to demonstrate high power coherent radiation amplification at 34.95 GHz. Experiments show a saturated efficiency of 37%, a bandwidth of 0.36%, and a gain of 23.6 dB corresponding to peak radiation output power of 210 kW. Experimental results are in good agreement with large signal simulations. Calculations also show that a stagger-tuned three-cavity circuit increases the bandwidth to more than 0.9%.

Demonstration of a 10 kW average power 94 GHz gyroklystron amplifier

The experimental demonstration of a high average power W-band (75–110 GHz) gyroklystron amplifier is reported. The gyroklystron has produced 118 AW peak output power and 29.5% electronic efficiency in the TE011 mode using a 66.7 kV, 6 A electron beam at 0.2% rf duty factor. At this operating point, the instantaneous full width at half-maximum (FWHM) bandwidth is 600 MHz. At 11% rf duty factor, the gyroklystron has produced up to 10.1 kW average power at 33% electronic efficiency with a 66 kV, 4.15 A electron beam. This represents world record performance for an amplifier at this frequency. At the 10.1 kW average power operating point, the FWHM bandwidth is 420 MHz. At higher magnetic fields and lower beam voltages, larger bandwidths can be achieved at the expense of peak and average output power.

UV-LIGA microfabrication of 220 GHz sheet beam amplifier gratings with SU-8 photoresists

Microfabrication techniques have been developed using ultraviolet photolithography (UV-LIGA) with SU-8 photoresists to create advanced sheet beam amplifier circuits for the next generation of vacuum electron traveling wave amplifiers in the 210–220 GHz (G-band) frequency regime. We describe methods that have led to successfully fabricated millimeter wave circuits, including applying ultra-thick SU-8 photoresist layers on copper, copper electroforming solutions, and the challenging removal of the SU-8 photoresists. A table of experimental liquid SU-8 removal chemistries and results is also presented.

Development and demonstration of high-average power W-band gyro-amplifiers for radar applications

The results of a focused program to develop high-power W-band gyro-amplifiers, which culminated in the demonstration of record average output powers from amplifiers in this band, are described. Following an experimental and theoretical study of low-duty prototype amplifiers, two high-average power devices were designed, built, and demonstrated. The first high-average power amplifier achieved 10.1-kW average output power at 33% efficiency in the TE/sub 0.1/ mode at 93.8 GHz. The instantaneous bandwidth was 420 MHz and the saturated gain at the 10.1-kW point was 32 dB. The second high-average power gyroklystron, designed for improved bandwidth, demonstrated 10.2-kW average power at 31% efficiency with 700-MHz instantaneous bandwidth and 33-dB saturated gain. The measured results of the low-duty prototype amplifiers and the high-average power gyroklystrons are described in detail. In addition, theoretically predicted results for a high-average-power W-band gyrotwystron amplifier, which is currently in construction, are presented.

Open-ended coaxial probe for high-temperature and broad-band dielectric measurements

A stainless steel open-ended coaxial probe was developed to measure the complex permittivity of solid dielectric materials at elevated temperatures and over a broad frequency range. The spring loading of the inner conductor insured that the probe maintained contact with the sample up to 1000/spl deg/C and eliminated errors due to differential thermal expansion of the probe. Comparison with an industry standard probe demonstrated that the spring-loaded probe accurately and reproducibly measured the complex permittivity of several samples over a broad frequency range of 0.3-6 GHz at room temperature. At temperatures up to 1000/spl deg/C, dielectric measurements of a glass ceramic and of a porous alumina composite performed with both a spring-loaded probe and a resonant cavity agreed to within 8% for the real part and 15% for the imaginary part of the complex permittivity. The probes insensitivity in measuring low-loss materials constrained accurate dielectric measurements to materials with tan /spl delta//spl ges/0.05. Finally, optimization of an open-ended probe by varying the probe dimensions is presented.